I've found that it's dangerously easy to fall asleep while driving long distances. But it's not a sound sleep, I always felt myself fall asleep and woke myself up just when it happened. As a passenger I have a harder time falling asleep. I would try doing something to be really exhausted at the start of the car ride, then try to stay awake as long as you can until you really can't stay awake any longer. Then just lean against a pillow and try a WILD. If that fails, there's always DILD.